1. Field of the Invention
The invention relates to water purification and more particularly relates to methods and compositions for disinfecting water in swimming pools.
2. Brief Description of Related Art
The water contained in swimming pools of any size need not be of potable quality but for aesthetic and hygienic reasons it is desirably maintained free of solid and microbiological contaminants. Normal maintenance may include filtration, for example through sand, diatomaceous earth or cartridge filters and treatment with a biocide such as chlorine or chlorine containing compounds.
In recent years, the art has sought to replace chlorine as a pool water disinfectant because of certain disadvantages associated with its use. For example, chlorine in biocidal (germicidal) concentrations may be an irritant to human bathers. Also, chlorine in water will react with many organic compounds which may be present in the water, to produce chlorinated derivatives commonly referred to as "haloforms"; see Rook, "Formation of Haloforms During Chlorination of Natural Waters", J. Water Treatment Exam., 1974, pp. 234-243. These haloforms, for example chloroform, methyl chloride, carbon tetrachloride, chloroacetone and the like may be hazardous to humans and their formation in swimming pool water is to be avoided. Chloramines are also formed, which are responsible for skin, eye and raucous membrane irritations and the odor of chlorine associated with many swimming pools. Removal of dissolved haloforms generally requires aeration, which also removes substantial quantities of the chlorine. In such a system, the chlorine must be replenished at frequent intervals so as to maintain a concentration of from about 0.5 to 20 ppm.
Other processes based on the use of an oxidizing agent for germicidal activity include the use of inorganic peroxy acids such as peroxymonosulphuric acid or peroxymono- phosphoric acid. However, these acidic products are relatively poor germicides and are not stable in alkaline or neutral waters such as swimming pool water.
indirect oxidants such as sodium hypochlorite (bleach) are also well known germicides but they generally are highly alkaline compositions (to maintain stability) and may cause precipitation of water-hardness salts present in the water, and may cause changes in pH which must then be readjusted with a suitable acid.
Certain selected quaternary ammonium compounds have also been used for their bactericidal activity in water supplies; see for example the descriptions given in U.S. Pat. Nos. 3,332,871; 4,539,071; and 4,925,866. These compounds are generally non-irritating to humans and odor free. However, their effectiveness in water is somewhat limited to soft (low calcium content) or distilled waters. Efficacy generally decreases when the treated water is hard or has an appreciable calcium content, for example at levels of about 300 mg/liter or more.
We have discovered that a particular combination of selected quaternary ammonium compounds and an oxidizer shows unexpected antibacterial activity, even in hard waters.